Cash for Conviction Rates?

This story is a few days old, but I flag it because while I was initially very skeptical, I am now somewhat uncertain.  A DA in Colorado has instituted a system of bonuses for line ADAs: try at least 5 cases a year (that is not a large number, in my experience), reach a conviction rate of at least 70%, and receive a bonus in the range of about $1,000 to $3,000.

One important thing that will color any assessment of this plan is that we are talking about conviction rates and not total convictions (the title of the piece is potentially misleading).  One might think that to the extent that the bonus system conditions a prosecutor's discretion about whether to bring a case at all, it might be a good thing.  Also, and as a general matter, we want prosecutors to give better deals for weaker cases, and to try stronger cases, so perhaps the incentives in this kind of system may match up with the public interest.

On the other hand, it is certainly possible that the bonus system might make a prosecutor push to try a case that ought really to settle, thereby misallocating resources in an already resource-strapped system.  On the third hand, it might be thought a good thing to provide incentives for more cases to be tried, since the risk aversion of prosecutors to trials, and the deleterious effects on the development of criminal law, is problematic (thanks to Mike Simons for this thought).  On the fourth hand, suppose the year is coming to a close, and a line ADA has not met his quota.  Wouldn't that ADA have incentives to go for broke and try a whole string of cases, because a few more losses would not affect his salary, but a few more wins might vault him "into the bonus"?  Finally (5th hand), who makes the decision about when to try?  The DA herself, or the line ADA?  I can see problems here if the discretion about whether to push for trial is solely (or even mostly) in the DA's hands.

There are also potential difficulties under the ethics rules (Rule 3.8 and maybe even Rule 1.5's proscription against contingent fees in criminal cases) that are implicated.  Thoughts about the justifiability of this scheme?